Cretaceous Period Key Facts
Timescale: 144 million years ago to 65 MYA.
Environment: dispersing continents; tropical, sub-tropical, arid and temperate climates; cool polar conditions.
Notable dinosaurs: Tyrannosaurus rex, Velociraptor, Triceratops.
Other animals: mammals; flying reptiles (pterosaurs); birds; insects; marine life.
Cretaceous Period dinosaurs were many and varied. But they were also doomed. A mass extinction event at the close of this period spelled the end for dinosaurs. Before they bowed out, however, the dinosaurs gave us a truly memorable beast - Tyrannosaurus rex.
Familiar world?
During the early Cretaceous, there were two large continents, Gondwana to the south (comprising South America, Africa, peninsular India, Australia and Antarctica) and Laurasia to the north (comprising North America, Europe and Asia). By the end of the period, these vast landmasses had sub-divided and moved much closer to their present positions. Australia was still connected to Antarctica, though, and India had not yet joined Asia. Overall, it was one of the warmest times in Earth's history, except for the polar latitudes, where scientists believe temperatures dropped below 0 degrees Centigrade during winter.
Enter the king
If there's one dinosaur that everyone's heard of, it's Tyrannosaurus rex ("tyrant lizard king"). This terrifying predator evolved during the late Cretaceous and grew to 12 metres. It weighed around 5 tonnes and could open its massive jaws an eye-watering 1 metre wide. Those jaws, with their strong teeth, weren't just capable of ripping flesh. They could crunch through bone, too! But Tyrannosaurus wasn't all brute force. It had acute, binocular eyesight, ultra-sensitive hearing and a highly developed sense of smell that may have helped it locate dead animals it could scavenge, as well as live prey. Like Allosaurus from the Jurassic Period, it seems that Tyrannosaurus may also have looked after its young.
Killer speed merchant
Compared to Tyrannosaurus, Velociraptor ("quick plunderer") was a lightweight at just 1.8 metres and 7kg - 15kg. But what Velociraptor lacked in size it made up for in ferocity and killing efficiency. And speed. Velociraptor could reach speeds of 64kph, using its tail as a counterbalance on tight turns. In addition to a mouthful of razor-sharp teeth, Velociraptor had huge claws on its feet and hands. It used these to climb up larger prey. As if one Velociraptor on its own wasn't enough, these vicious late Cretaceous killers hunted in packs. And we all know how scary that can be from watching Jurassic Park...
Don't call me frilly
Triceratops ("three-horned face") is the most famous of the horned dinosaurs. This late Cretaceous animal grew to around 9 metres and weighed up to 10 tonnes. As well as three deadly horns, Triceratops had an impressive bony frill behind its head. Palaeontologists believe this was used in courtship and in ritual combat with rivals. Triceratops was a herbivore. Its jaws ended in a quasi-beak that would have helped it gather tough vegetation. Palaeontologists have established that many horned dinosaurs were herding animals but no Triceratops fossils have ever been found together. It seems that Triceratops was a bit of a loner.
Up, up and away
The skies above late Cretaceous dinosaurs were busy. Pterosaurs, huge flying reptiles with wingspans of up to 12 metres, had once been numerous but were on the decline during the late Cretaceous. Their place was being taken by direct descendents of dinosaurs - birds. Birds had evolved from the theropod group of dinosaurs, which included bipedal predators such as Velociraptor and Tyrannosaurus rex. By the late Cretaceous, birds were widespread in forests and mudflats. Some resembled modern birds, such as curlews and sandpipers. There was even a forerunner of today's parrot family.
The great extinction
We don't know what caused it but, at the end of the Cretaceous, there was large-scale extinction in marine and terrestrial life. Other life-forms, including reptiles and mammals, survived but dinosaurs - except for birds, of course - became extinct. Debate over the cause of this mass extinction is intense. Some scientists believe that an increase in volcanic activity, together with the effects of the shifting continents, caused profound climate change on Earth. Another theory is that a massive extraterrestrial object hit the planet, throwing up a huge dust cloud that obscured the sun, triggering climatic changes. Whatever the explanation, the age of the dinosaur was over.
Quick dino-facts
Traditionally, the arms of Tyrannosaurus were thought to be weak and useless. Now, palaeontologists believe there's evidence that these arms were strong, with nearly opposable fingers. No one's sure what T. rex used his strong little arms for, though!
Much of the evidence on the diet of dinosaurs comes from the study of their fossilised dung.
The Velociraptors in Jurassic Park were portrayed at twice their actual size.
Jurassic Period Key Facts
Timescale: 206 million years ago (MYA) to 144 MYA.
Environment: closely grouped continents; tropical, sub-tropical, temperate and arid climates.
Notable dinosaurs:Diplodocus, Brachiosaurus, Stegosaurus, Allosaurus.
Other animals: early mammals; flying reptiles (pterosaurs); early birds; insects; marine life.
There had been no holding back dinosaurs by the end of the Triassic Period. Then, during the Jurassic Period, they became the dominant animal life-form on the planet. Not only that, but Jurassic dinosaurs were big - very big. Giant herbivores, known as sauropods, evolved during the Jurassic. They were the largest land animals ever to walk the Earth.
An evolving world
Jurassic Earth was on the move. The Pangaea super-continent began to split into two during the mid-Triassic and this trend continued during the Jurassic Period. As early versions of today's continents moved away from each other, the oceans began to exert more influence on Earth's weather: the climate became far more varied. Vegetation was becoming more sophisticated, too. Palm-like plants and conifers flourished. Some experts also believe that the first flowering plants developed at the end of the Jurassic.
Land of the giants
The late Jurassic Period is renowned for huge dinosaur herbivores, known as sauropods. The largest grew to more than 40 metres in length and probably weighed up to 100 tonnes. You wouldn't have wanted one of these titans to step on your toe but sauropods weren't as heavy as their size might have suggested. They were actually quite lightly built creatures: much of their apparent bulk was due to internal, air-filled sacs.
Not walking in water
Palaeontologists used to believe that sauropods were amphibians. Artists' impressions of the large herbivores always depicted them grazing in lakes. It wasn't thought possible that sauropods could support their supposed vast weight without the buoyancy of water. Today's dinosaur experts are confident that sauropods had legs that were akin to a modern elephant's - easily able to support their own body weight.
Huge herder
Long-necked and long-tailed, Diplodocus ("double beam") is probably the best-known sauropod. Herds of these giant dinosaurs dominated the late Jurassic period. They were so big (25 metres and over) that they would have changed the landscape around them. To get at its food, diplodocus tore up saplings and pushed over trees, creating open plains. Everything about diplodocus was big - even its eggs were a hefty 25 centimetres across.
Tree grazer
Brachiosaurus ("arm lizard") was another well-known late Jurassic giant. Tall rather than long, brachiosaurus could grow up to 30 metres. It had a long neck that allowed it to graze among treetops and long legs that kept its body high off the ground. Its front shoulders were higher than its haunches, giving it a sloped appearance rather like a modern giraffe.
Plated-up
Stegosaurus ("roof lizard") was a medium-sized herbivore of the late Jurassic. Around 7 metres long and up to 3 tonnes in weight, Stegosaurus had a series of large, bony plates running along its spine. Experts have suggested several uses for these plates. They could have been used in courtship display or they may have served as heat-regulating devices. Perhaps they were defensive armour or maybe Stegosaurus could have made itself more terrifying in combat by pumping the plates with blood. At any rate, Stegosaurus was no pushover in the dangerous world of Jurassic Earth. It had a fearsome defensive weapon - a powerful, spiked tail that could deliver crippling blows to would-be predators.
Jurassic slasher
As large herbivores became more prevalent, bigger predators emerged, too. Allosaurus ("other lizard") was the commonest large predator of the period. Around 12 metres long, it is known to have preyed on big sauropods as well as smaller animals. Its curved teeth and huge jaws inflicted deep slashing wounds on its victims. You wouldn't last long once you were corned by an Allosaurus. Nimble prey might have outrun this predator, though, because it wasn't capable of sustained bouts of speed. Interestingly, there is some evidence that Allosaurus cared for its young, bringing back meat for its offspring, who lived in a protected den until they were old enough to fend for themselves.
Quick dino-facts
Three stars of Jurassic Park - Triceratops, Tyrannosaurus rex and Velociraptor - weren't actually around during the Jurassic Period. They didn't evolve until the late Cretaceous.
After studying fossil tracks, modern palaeontologists concluded that giant sauropods walked with their tails held aloft, not dragging along the ground.
Giant sauropods had large stones in their stomachs to help them digest tough vegetation.
Triassic Period Key Facts
Timescale: 248 million years ago (MYA) to 206 MYA.
Environment: one continent (Pangaea), that began to break up; hot, semi-arid, seasonal rainfall.
Notable dinosaurs: Coelophysis, Plateosaurus.
Other animals: crocodile-like terrestrial predators; beaked herbivores; flying reptiles (pterosaurs); proto-mammals; insects; marine life.
The Triassic Period was the first period of the Mesozoic Era, which ran from 248 million years ago (MYA) to 65 MYA. A lot happened to Earth and its life-forms during the Triassic but the most celebrated event was the evolution of dinosaurs. These remarkable creatures emerged around 230 MYA and dominated the planet until the end of the Mesozoic Era.
One world, one continent
Planet Earth looked very different at the beginning of the Triassic Period. There was just one landmass, a huge continent known as Pangaea. It stretched from pole to pole and included a vast desert at its centre. There was no grass, although ferns and mosses provided ground-cover in less arid areas. Pangaea began to break up in the mid-Triassic.
Extinction event
Just before the beginning of the Triassic, Earth experienced its largest mass extinction. More than 90% of the planet's life-forms at sea and on land were extinguished. Geologists are divided over the cause - or causes - of this momentous crisis. Possible explanations include glaciation, climatic fluctuation and large-scale volcanic activity. Whatever the reason, it seems likely that the drastic reduction in the diversity of animal life contributed to the rise of the dinosaurs.
Rival relatives
During the first half of the Triassic, however, dinosaurs were still a long way from ruling the Earth. They had a variety of competitors, including close relatives from the same animal group that dinosaurs themselves belonged to, the archosaurs ("ruling reptiles"). Crocodile-like terrestrial predators were among the most successful of these archosaur rivals but they had died out by the end of the Triassic.
Strange beast
One of the oddest creatures that shared the planet with early dinosaurs was Placerias. It must have looked like a cross between a hog, a cow and a turtle. Placerias was a large, herding herbivore with a horny beak and a pair of downward-pointing tusks. It was a dicynodont ("two dog-teeth") - a group of animals that shared common ancestors (the synapsids) with modern mammals. Palaeontologists believe Placerias ate low-growing plants, as well as using its tusks and beak to grub for roots and tubers.
Slim and dangerous
One of the first true dinosaurs was Coelophysis ("hollow form"), a carnivorous, bipedal predator that emerged in the late Triassic, 225-220 MYA. Hollow-boned Coelophysis grew up to 3 metres in length, weighed around 27kg and probably fed on smaller reptiles and amphibians. It had curved claws on its hands and a slim head crammed full of very sharp teeth. Some experts have suggested that Coelophysis could bring down bigger animals by taking slashing bites out of their legs or sides. Fossil Coelophysis skeletons have been found in the same locations, so it's possible that these dinosaurs may have herded, although there's no firm evidence that they hunted in packs.
First of the giants
Around 210 MYA, a new type of dinosaur emerged - the giant herbivore, Plateosaurus ("flat lizard"). Weighing around 3 tonnes and growing up to 7 metres, Plateosarus was a forerunner of the huge Jurassic Period dinosaurs. It had a long, powerful tail and a set of coarsely serrated teeth for chewing tough vegetation. Plateosaurus also had a large, curved claw on its thumb. We're not sure whether this was used for food collection or defence.
Waiting in the wings
Dinosaurs were the big success story of the Triassic but another group of animals was beginning to emerge, too. These were the cynodonts, small, mammal-like creatures that lived in burrows. They probably laid eggs but, after years of debate, most experts now believe that the cynodonts were warm-blooded.
Extinction returns
An extinction event just before the Triassic began had given dinosaurs a leg-up on to the evolutionary ladder. As the period came to a close, another extinction event occurred. Geologists don't know what caused it but, once again, large numbers of sea and land animals were wiped out - although the effects are not believed to have been as severe as the extinction event just before the Triassic Period opened. In any event, dinosaurs came through the crisis stronger than ever, setting the stage for an explosion in numbers and diversity.
Quick dino-facts
Dicynodonts were very successful before they died out. Early Triassic dicynodont remains have been found in South Africa, India, China, Russia, Australia and Antarctica.
Experts believe that Coelophysis was a cannibal that preyed upon its own young during lean times.
Large numbers of Plateosaurus skeletons have been found in the same location, suggesting they may have herded. Alternatively, instinct drew them to the same place to die...
What really killed the dinosaurs?
Earth's history has seen countless mass extinctions but the most talked about happened 65 million years ago during the late Cretaceous period, ending the reign of the dinosaurs. In fact, whatever caused the death of the dinosaurs also caused the death of around 70 per cent of all species on Earth. We look at some of the theories put forward.
Comet and cosmic rays killed the dinosaurs
The theory: A massive comet travels close to Earth every 26 million years, bringing with it radioactive debris that collides with our planet, disrupting weather patterns and wiping out entire species, just as it did the dinosaurs some 65 million years ago. How likely? We have no concrete evidence of extraterrestrial events occurring at the point of dinosaur extinction. Furthermore, dinosaur remains show no evidence of radiation damage. An asteroid impact killed the dinosaurs
The theory: A large asteroid struck Mexico, forming a 240 kilometre wide crater. Resulting debris created a deposit of white powder in the atmosphere. This 'nuclear winter' blocked out the sun, killed plants, then plant-eaters and, finally, meat-eaters. How likely? Those dismissing the theory claim that smaller reptiles like turtles, alligators and crocodiles would also have been harmed; others argue the crater simply wasn't large enough to have caused such devastation.
Volcanos killed the dinosaurs
The theory: Western India saw huge volcanic eruptions which unleashed enormous quantities of lava, blocking out the sun, causing widespread climatic change and wiping out the dinosaurs. How likely? Deadly iridium in the Earth's 'K-T boundary' could conceivably have been caused by lava eruptions. However, scientists have widely agreed that 65 million years ago there was a global fall in temperature; a volcanic eruption would have had the opposite effect. An ice age killed the dinosaurs
The theory: Ice ages have occurred throughout Earth's history, with the last one ending about 10,000 years ago. A very severe ice age altered climates and froze waters to the extent that dinosaurs were unable to weather the conditions, and slowly died out. How likely? This theory has been largely discarded for one simple reason: scientists have not found a single scrap of evidence of an ice age occurring during the life of the dinosaurs. Hay fever killed the dinosaurs
The theory: Flowering plants known as angiosperms arose around 65 million years ago, creating a mass allergic reaction among dinosaurs. How likely: Not very! Flowering plants were around for millions of years before the dinosaurs disappeared and we have no evidence whatsoever that their pollen was capable of killing the dinosaurs. Plus this wouldn't explain the massive marine extinction - there have never been any marine angiosperms.
Obesity killed the dinosaurs
The theory: The dinosaurs got too big and heavy, so much so they couldn't move about, defend themselves or withstand their own weight! How likely? There is absolutely no evidence to suggest the dinosaurs became so large and cumbersome that they couldn't move. Simply put, it is an evolutionary impossibility. Besides, most dinosaurs around by the end of the Cretaceous period were of medium or small size.
Mammals killed the dinosaurs
The theory: The ecosystems of Earth 65 million years ago were such that mammals were out-competing the dinosaurs for food and space. How likely? Evidence points to a simultaneous evolution in dinosaurs and mammals, and some believe mammals did eat dinosaur eggs. But it's unlikely that mammals and dinosaurs had similar diets, so competition wouldn't have occurred. And there were no marine mammals at the time, so they couldn't have wiped out marine reptiles. Disease killed the dinosaurs
The theory: Towards the end of the Cretaceous period, land bridges opened up between places such as Asia and North America, allowing species to migrate. This led to a spread of disease to which other animals were not resistant. How likely? It could happen - Native Americans were nearly wiped out by smallpox, while the European invaders were resistant. But this argument fails to explain the disappearance of a multitude of species that lived in the sea. Climate change killed the dinosaurs
The theory: Earth gradually changed in climate over a long time period and the dinosaurs were not able to adapt to the cooler, drier climate. How likely? Climate change could have come about because Earth somehow tilted over about 23.5 degrees around 65 million years ago. How likely? Tilting could have occurred but what could have caused it. Asteroid impact? Debris from a passing comet? Scientists have never been able to answer this question.
Nothing killed the dinosaurs!
The theory: Dinosaurs were not wiped out, they evolved into birds. There were certainly feathered dinosaurs and early birds resembled small meat-eating dinosaurs. Could it be that dinosaurs still walk – or fly – among us? Most scientists agree there is considerable evidence for many species of carnivorous theropod dinosaurs such as Velociraptor evolving into birds. But not all dinosaurs evolved into birds; Tyrannosaurus Rex died out with no evolutionary trace.
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